This application claims the priority of 198 18 035.7 filed Apr. 22, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a transversal flux machine and a rotor arrangement for a transversal flux machine.
Permanent-magnet-excited synchronous machines according to the transversal flux concept are generally known and permit high force densities with high efficiency.
A transversal flux machine of the aforementioned type is described in European Patent Document EP 0 677 914. The transversal flux machine according to this document has a stator and a rotor as well as magnetic circuits. The flux of the magnetic circuits extends essentially transversely to the movement direction of the rotor. The stator has E-shaped pole elements, in the case of which the central pole shanks are arranged offset by one pole pitch with respect to the outer pole shanks. The permanent magnets of the rotor essentially have a cubical construction and are situated in their flux direction perpendicular to the adjoining pole surfaces of the pole elements, while they rotate between two shanks respectively of the E-shaped pole elements.
International Patent Document WO 90/09697 describes a permanent-magnet-excited electric machine which has an outer stator and at least one coaxial inner stator. A rotor rotates between these with two parallel rows of permanent magnets which extend at an axial distance from one another. Permanent magnets adjacent in the circumferential and axial direction have different polarities.
For the industrial manufacturing of such a machine, the outer stator and the inner stator are each constructed in three parts including a yoke ring and two laminated pole rings. The pole rings carry radially projecting pole teeth which are arranged in the rotating direction at a spacing of one pole pitch respectively. The laminated and segmented pole rings are pressed in the radial direction against the yoke ring and are supported in the axial direction on a ring web radially projecting from the yoke ring. One winding half-branch respectively of a ring-shaped pole winding is situated between the pole rings and the ring web. The winding half-branches in the outer and inner stator each form the pole winding.
International Patent Document WO 88/06375 discloses an electric machine in a transversal flux construction, in which an improvement is provided wherein the pole arrangement has an identical construction on the whole circumference and leakage flux components in the longitudinal direction are avoided. By means of this arrangement the magnetic resistance for the field components is reduced.
International Patent Document WO 95/04399 describes a transversal flux machine, wherein several winding branches are provided in the stator in the form of ring-shaped coils arranged coaxially with respect to the machine axis. These are embedded within sequences of C-shaped soft-iron elements arranged in the circumferential direction. The rotor and the partial rotors consist of permanent magnet elements and flux-guiding soft-iron elements which rotate in groove-type recesses of the soft-iron stator elements.
European Patent Document EP 0 712 199 illustrates a transversal flux machine with a number of outer soft-iron stator elements, with a plurality of inner soft-iron stator elements, one ring winding respectively of the outer and inner stator, and a rotor which, in turn, consists of mutually alternating magnets and soft-iron elements. In the case of this transversal flux machine, the magnets taper from the outside to the inside, and the width of the inner soft-iron stator elements is smaller than the width of the outer soft-iron stator elements.
All of the above-mentioned transversal flux arrangements have the disadvantage that their construction is not sufficiently stable in the transition area from the stator to the rotor. As a result, vibrations caused by the locally constantly changing attraction ratios between the rotating rotor and the stator, undesirable noises are developed. In addition, no optimal cooling is ensured in the case of the above-discussed transversal flux machines. Specifically, in the case of high-power transversal flux machines, noise development may occur which is of such a magnitude that efficiency deteriorates because of the higher conductor resistance and because the machine supplies less power because the magnetic properties deteriorate at higher temperatures. In an extreme case, its operability may even be endangered. In addition, the maximal constant power is lower while the cooling is insufficient.
It is an object of the invention to further develop a transversal flux machine of the aforementioned type, which generates little noise in its operation, so that mechanical stability, efficiency and capacity are increased and a functionally reliable operation can be ensured in the high-power range. In addition, a simple and low-cost manufacturing is permitted.
According to the present invention, this object is achieved by a transversal flux machine wherein, a retaining ring is provided on the stator side in each case between the ring winding and the rotor arrangement. The retaining ring has equidistantly spaced recesses at its two edge areas for receiving teeth of a pole or a pole system which project in the direction of the rotor arrangement.
The retaining ring is used for stabilizing the totality of the pole system and the ring coil so that, during an operation of the transversal flux machine, the individual pole elements move neither in the direction toward the rotor nor parallel thereto. Thus, vibrations are avoided in the stator range which may result in an increased generation of noise.
In addition, the retaining ring provides thermal shielding of the rotor and the stator so that heat generated in the stator arrangement cannot be transmitted unhindered to the rotor.
The intensity of the magnetic flux currents in the rotor--thus in the permanent magnets and the soft-iron reflux elements--depends on the temperature of the permanent magnets. In particular, the magnetic properties deteriorate as the temperatures rise. Starting at defined limit temperatures, the magnetic properties of the permanent magnets are lost completely. The above-mentioned shielding is therefore particularly advantageous in the case of high-power transversal flux machines, in the case of which--at least on the stator side, a high heat development takes place.
In addition, it is possible to cool the retaining ring. In this case, the heat generated in the stator can be carried away in a simple manner, thereby increasing the maximal constant power of the whole arrangement. The shielding between the stator and the rotor is further increased by this measure.
According to an advantageous embodiment, cooling of the retaining ring can be achieved in that at least one cooling duct is constructed in this retaining ring. When a suitable liquid flows through the cooling duct, the heat can be carried away in a simple and efficient manner.
The retaining ring represents an optimal winding carrier for the ring coil but also the pole system so that, overall a compact total unit can be provided which is easy to manufacture.
In a preferred embodiment, the recesses in the retaining rings are constructed to be tapering, for example, essentially conically, in the direction of the rotor arrangement. By means of a complementary construction of the teeth of the pole system received in the recesses, the stability of the overall arrangement, particularly in the direction of the rotor, can be further improved. Furthermore, the induction decreases in the conical teeth. Also, the whole circumference of the machine is available for guiding the flux in the pole yoke. The thickness of the pole yoke in the radial direction is not subjected to any limitation, so that arbitrary values of the induction can be set in the pole yoke. This leads to lower iron losses, which is advantageous in the case of a machine which is to be operated at high frequencies.
According to another embodiment, the retaining ring consists of a ceramic material. Such a material combines the characteristics of high mechanical stability, electric inactivity, good thermal conductibility and/or non-magnetic material. The cooling ducts in such a retaining ring can be produced by joining two retaining ring parts, at least one part having surrounding, for example, groove-shaped recesses.
With a view to a particularly simple variant at reasonable cost, each pole system preferably consists of a ring-shaped pole yoke and two laterally adjoining pole rings. Each of these three parts can be produced separately, for example, by joining individual metal sheets or winding up a sheet metal strip. The pole rings can be produced like conventional sheet metal blanks by punching.
In the pole yoke-side area, the pole rings are preferably perforated by incisions or slots. Such a measure reduces the occurrence of eddy currents during the magnetic flux transition from the pole yoke to the pole rings or vice versa, so that losses can be minimized.
In a particularly simple embodiment of the invention, the individual stator elements, such as the pole yoke, the pole rings, the ring coil and the retaining rings are constructed as separate parts at a reasonable which are held together by means of a stator housing. A transversal flux machine of this type can be produced particularly easily.
The generation of noise can be reduced when the area of the stator arrangement facing the rotor has a smooth surface. This surface is composed of the side of the retaining ring or rings facing the rotor as well as of the surfaces of the teeth of the pole rings which face the rotor.
Another cooling possibility is obtained if at least one cooling duct is constructed in the stator housing. If several cooling ducts are constructed in the stator housing as well as in the retaining ring, the whole stator arrangement can be cooled in an extremely effective manner.
For solving the above-mentioned problems a stable arrangement must not only be ensured on the stator side but also on the rotor side. Thus, according to another aspect of the invention, the above-described object is provided by means of a rotor arrangement wherein the row of alternatingly arranged permanent magnets and soft-iron reflux elements extending in rotating direction is held by a rotor support which has on each side an outer fastening ring with a projection extending at its stator-side outer end axially toward the inside. This measure prevents that the individual elements, particularly permanent magnets and soft-iron reflux elements, move in the direction of the stator as the result of attracting or centrifugal forces.
If two rows of alternatingly arranged permanent magnets and soft-iron reflux elements extend in parallel next to one another, a central fastening ring is preferably provided in-between, and a ring-shaped holding band can be arranged at the stator-side outer end. Like the projection of the outer fastening ring, the ring-shaped holding band is used for fixing the rotor elements, particularly against a movement in the direction of the stator.
In a particularly preferred embodiment, recesses, which in the center fastening ring are spaced equidistantly from one another, are provided at the level of the soft-iron reflux elements for receiving permanent magnets. The arrangement of the permanent magnets in the recesses of the central fastening ring further increases the capacity of the machine.
A reduced straying of the magnets which are not situated in the recesses of the central fastening ring is achieved by a lengthened construction of the permanent magnets in the radial and/or axial direction with respect to the soft-iron reflux elements.
The quiet running of the transversal flux machine can be further increased particularly by a plane construction of the stator-side surface of the rotor.